Hmmm. Video game player killing people with hammer. Should my parents now be concerned that I recently purchased a replica 14th century warhammer? (of course it was back-ordered so I don't have it yet.

5 days left until the earliest time it could arrive)
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I think that the blame wholy falls on the parents in this case.
Obviously, as has been stated, the media does not do an accurate job of portraying the consequences/side effects of the actions. (Another point for Freespace - the human cost is told somewhat. "We lost a place many of us called home. We lost entire squadrons, the Colossus and most of our fleet. We lost so many friends that we celebrate our victory with grief and mourning." "I'm goin down! I'm goin down!" "AAHHHH!")
But, the parents SHOULD control what their children are exposed to, and teach them what things are good for them, and what things are bad. The mother had to leave the courtroom because it was too horrible for her? Well, Mom, didn't you know what kind of games your kid was playing? Yes, parents can go overboard and be too controlling, causing the kids to rebel, which is also bad. But just letting the kids do whatever they want?
Kids, especially younger ones, have no common sense. It is the job and responsibility of the parents to impart wisdom and common sense to them. When I was six years old, I decided it would be fine to walk across the frozen swimming pool in our back yard. Smart thing? No. Would I still do it today? No. Would I have tried it again if my parents had just told me, "You know, Mark, that wasn't a very smart thing to do" and left it at that? possibly. Instead, I got grounded for a week. And, after establishing that walking across the swimming pool is something that leads to punishment, my parents explained to me why it was a bad thing.
I had about a month's worth of lectures from my parents when I bought my first sword four or five years ago. (Think I was 16 at the time, maybe 15). They knew I wanted it, and let me get it, but made very sure I knew that going down the street chopping people's heads off with it was not a good idea.
Unless the parents give the children a good moral foundation, there's always going to be problems. Proverbs 22:6 says it all - "Train up a child in the way he should go, and when he is old he will not depart from it." I'd never heard of Manhunt before reading the article, and don't think I'll ever play it, because my parents made sure I wasn't exposed to violence much in my childhood, until I could understand the human costs and consequences involved. I've no interest in bludgening people over the head with a hammer for fun.
And I'm willing to bet my life that if Warren's parents had paid attention to the types of activities in his life, and given him a moral foundation ten to fifteen years ago that he would not have committed this crime.
Phillipians 4:8 - "Finally, brethren, whatsoever things are true, whatsoever things are honest, whatsoever things are just, whatsoever things are pure, whatsoever things are lovely, whatsoever things are of good report; if there be any virtue, and if there be any praise, think on these things."
This would have solved the whole problem.